The following relates to the electrical power arts. It particularly relates to monitoring a safe electrical disconnection of a high voltage circuit for servicing, and will be described with particular reference thereto. However, the following will also find application in routine monitoring of electrical line voltages and in other aspects of electrical safety.
To ensure safety during servicing of electrical systems and circuits which carry high voltages, a “lockout/tagout” procedure is typically followed. A circuit breaker or ON/OFF switch that delivers power to the circuit to be serviced is opened or disengaged to disconnect electrical power from the circuit, and the breaker is physically locked into the opened or disengaged position using a padlock or other device (the “lockout”). Additionally, the servicing electrician affixes a tag to the physically locked breaker that provides information such as the electricians' identity and contact information, service authorization information, and the like (the “tagout”). The tag typically is bright red or otherwise prominently displayed, and includes a plain language warning that only the installing electrician is authorized to remove the lockout/tagout and reenergize the circuit.
The lockout/tagout procedure greatly reduces the possibility of human error causing inadvertent application of power to the circuit under service. However, safety can be compromised even when the lockout/tagout procedure is properly followed, due to various potential sources of dangerously high voltages in the isolated circuit. For example, potential unexpected sources of DC energy include line capacitance, bypass capacitors, or power factor correction banks. Potential unexpected sources of AC energy include standby power generators, motor back-EMF, or human operation of an associated switch. Moreover, power ON/OFF switches or circuit breakers are not immune to failure, and the locked out breaker could potentially still be transmitting power.
Recognizing that the most dangerous power panel or box can be the one believed to be at zero energy potential, the Occupational Safety and Health Administration (OSHA) has issued regulation OSHA 1910.147 entitled “Control of Hazardous Energy (Lockout/Tagout)” which includes identification of residual or stored energy as a hazard. OSHA 1910.147 requires that electrical isolation be verified after lockout/tagout (LOTO). Furthermore, it requires that the verification of isolation continue throughout the electrical servicing if there is a possibility of reaccumulation of hazardous levels of stored energy.
To verify electrical isolation, electrical safety monitors which monitor electrical energy potentials of monitored electrical lines of an electrical panel are utilized. The electrical safety monitors provide a warning with light emitting diode (“LED”) indicators in response to an electrical potential being present on the monitored lines. During servicing, electricians verify normal operation of the indicators while the panel is powered and then verify all of the indicators are extinguished while the panel is powered down before opening the panel. Although electrical safety monitors have proven to be reliable, final verification by lack of illumination provides less assurance than desired due to the possibility of circuit failure or malfunction which could likewise be the culprit for extinguished indicators and not just the absence of voltage on the monitored lines.
Additionally, although the operating current required for indication is extremely low, typically less than 1 milliampere at 750VAC 3-phase, the electrical safety monitors are rated for 750VAC continuous operation and the monitored line voltages entering the monitor are at full 3-phase line voltage potentials. To further electrical isolate the electrical safety monitors due to the high energy potential during operation, the housing of these monitors are typically non-conductive and the electronics are fully encapsulated in a high quality thermoset potting compound. It is desired to have the electrical safety monitor include a separate internally mounted electrical package and an isolated remote display adaptor mounted in the panel to provide indication when an electrical potential is present on the monitored lines.
The following contemplates an improved apparatus and method that overcomes the aforementioned limitations and others.